feat(deeplink): add config merge command for preview

Expose config merging functionality to frontend for preview.
- Add merge_deeplink_config Tauri command
- Make parse_and_merge_config public for reuse
- Enable frontend to display complete config before import

src-tauri/src/lib.rs

@@ -706,6 +706,7 @@ pub fn run() {
             commands::sync_current_providers_live,
             // Deep link import
             commands::parse_deeplink,
+            commands::merge_deeplink_config,
             commands::import_from_deeplink,
             update_tray_menu,
             // Environment variable management